1. Field of the Invention
This invention relates to an image-forming method using a print medium and a transfer sheet film, for thermally transferring an image printed by using a sublimable dye ink from the transfer sheet film onto the print medium, to thereby form the image on the print medium, and the transfer sheet film used therefor, as well as to an image-forming apparatus.
2. Prior Art
Conventionally, an image-forming method is known which transfers an image printed on a transfer paper by using a sublimable dye ink by one of various printing methods from the transfer paper to a print medium. This image-forming method overlays a printing surface of the transfer paper to a transfer surface of the print medium, heating the transfer paper and the print medium while applying pressure thereto e.g. by using a thermal press, thereby causing the sublimable dye ink held in the transfer paper to permeate from the printing surface of the transfer paper in a direction of thickness thereof into the transfer surface of the print medium through evaporation/diffusion to effect image transfer. Then, after completion of the image transfer, the transfer paper is peeled off the print medium.
In general, to transfer a high-quality image printed on a transfer paper onto a print medium while maintaining the high quality of the image, it is essential to press the transfer paper and the print medium against each other for intimate contact there between during the image transfer operation. However, the transfer paper has too coarse a printing surface to achieve complete and intimate contact with the print medium, so that minute gaps are produced between the transfer paper and the print medium, resulting in a transferred image with color irregularity. On the other hand, if a transfer sheet having a smooth and solid surface is used to overcome the problem, since the transfer sheet has no elasticity differently from the transfer paper described above, it is difficult to cause air to be expelled from between the surfaces of the transfer sheet and a print medium held in intimate contact with each other. Therefore, in this case as well, it is expected to produce a transferred image with color irregularity.
It is an object of the invention to provide an image-forming method which is capable of improving image quality of a transfer image, and a transfer sheet film therefor, as well as an image-forming apparatus.
To attain the above object, according to a first aspect of the invention, there is provided an image-forming method comprising the steps of:
printing an image on a printing surface of at least one sheet of a transfer sheet film prepared in a manner associated with at least one surface of a print medium, by using a sublimable dye ink, thereby causing the sublimable dye ink to be held in the at least one sheet of the transfer sheet film;
overlaying the at least one sheet of the transfer sheet film to the print medium such that the printing surface of the at least one sheet of the transfer sheet film faces the at least one surface of the print medium;
transferring the image by heating the at least one sheet of the transfer sheet film and the print medium overlaid to each other while applying pressure thereto, thereby causing diffusion of the sublimable dye ink held in the at least one sheet of the transfer sheet film into the at least one surface of the print medium for color development; and
removing the at least one sheet of the transfer sheet film from the print medium having the image formed thereon,
wherein the transfer sheet film is formed of a water-soluble and soft resin material, and the printing surface is formed to be a smooth surface.
According to the image-forming method, when an image is printed on the transfer sheet film, the sublimable dye ink is impregnated into the transfer sheet film and held in the same. Then, the transfer sheet film and the print medium are overlaid to each other such that the printing surface of the transfer sheet film faces the surface of the print medium, and then heated in this state, whereby the sublimable dye ink is transferred from the transfer sheet film deep into the surface layer of the print medium as migration particles having sizes at a molecular level and develops color to form an image thereon. Then, simply by removing the transfer sheet film from the print medium thereafter, the print medium having the image easily formed on the surface thereof is prepared.
In the present image-forming method, since the transfer sheet film formed of a water-soluble resin material is employed as a transfer medium, it is possible to maintain excellent ink absorbency during the printing process, which enables the sublimable dye ink to be stably impregnated into the transfer sheet film and held therein without being diffused. Therefore, when the transfer sheet film is heated in a state overlaid to the print medium with its printing surface facing the same, the sublimable dye ink is transferred directly onto the surface of the print medium without passing through the transfer sheet film or being hindered by air or the like trapped between the transfer sheet film and the print medium, so that the print image can be transferred faithfully. Further, since the printing surface of the transfer sheet film has smoothness, and the transfer sheet film is formed of a soft resin, when the transfer sheet film is pressed against the print medium, air trapped between the transfer sheet film and the print medium can be expelled easily, which ensures as intimate contact as possible between the transfer sheet film and the print medium. This makes it possible to form a clear and sharp transfer image without color irregularity on the print medium. It should be noted that the transfer sheet film is preferably formed of a material composed of a main component of PVA (polyvinyl alcohol) and an additive which exhibits slight tackiness when heated.
Preferably, the printing step includes printing images on respective printing surfaces of two sheets of the transfer sheet film prepared in a manner associated with front and back surfaces of the print medium, by using the sublimable dye ink, thereby causing the sublimable dye ink to be held in the two sheets of the transfer sheet film, the overlaying step including overlaying the two sheets of the transfer sheet film to the print medium such that the printing surfaces of the two sheets of the transfer sheet film face the front and back surfaces of the print medium, respectively, the transferring step including transferring the images by heating the two sheets of the transfer sheet film and the print medium overlaid to each other while applying pressure thereto, thereby causing diffusion of the sublimable dye ink held in the two sheets of the transfer sheet film into the front and back surfaces of the print medium for color development, and the removing step including removing the two sheets of the transfer sheet film from the print medium having the images formed thereon.
According to this preferred embodiment, an image is printed on each sheet of the transfer sheet film, whereby the sublimable dye ink is impregnated into the sheet of the transfer sheet film and held in the same. Then, the two sheets of the transfer sheet film and the print medium are overlaid to each other such that the respective printing surfaces of the two sheets of the transfer sheet film face the front and back surfaces of the print medium, and then heated in this state, whereby the sublimable dye ink is transferred from the sheets of the transfer sheet film deep into each surface layer of the print medium as migration particles having sizes at a molecular level and develop color to form an image thereon. Then, simply by removing the transfer sheet film from the print medium, the print medium having the images easily formed on the front and back surface thereof is prepared.
Therefore, this preferred embodiment provides the same advantageous effects as described above, and is capable of forming clear and sharp transferred images without color irregularity on both sides of the print medium.
More preferably, the transferring step includes simultaneously pressing and heating front and back surface sides of the print medium overlaid with the respective two sheets of the transfer sheet film.
According to this preferred embodiment, it is possible to increase heat efficiency. Further, since the front and back surfaces of the print medium can be treated under identical hating conditions, it is possible to fix ink uniformly on both the front and back surfaces as well as to prevent warpage of the print medium due to heating.
Preferably, the transferring step includes the step of pressing and the step of heating, these two steps overlapping each other in timing such thin the step of pressing starts before the step of heating starts, and the step of heating ends before the step of pressing ends.
According to this preferred embodiment, in the step of transferring the image, it is possible to heat the transfer sheet film and the print medium after removing air or bubbles trapped at the interface between (or between the contact surfaces of) the transfer sheet film and the print medium by pressing the transfer sheet film and the print medium against each other. In short, it is possible to carry out heat treatment after having placed the transfer sheet film and the print medium in complete and intimate contact, which ensures excellent transfer of the image. Further, since the step of pressing ends after heating is completed, it is possible to suppress warpage of the print medium due to heating.
Preferably, the image-forming method further includes the step of removing air from an interface between the print medium and the transfer sheet film overlaid to each other, between the overlaying step and the transferring step.
According to this preferred embodiment, before starting the step of transferring the image, it is possible to sufficiently remove a small amount of air or microscopic bubbles remaining in the interface between the print medium and the transfer sheet film, which ensures further reliable intimate contact between the two and excellent transfer of the image by the following heat treatment.
More preferably, the step of removing air includes overlaying a soft cushion sheet to the print medium and the transfer sheet film overlaid to each other, and pressing the transfer sheet film against the print medium via the cushion sheet.
According to this preferred embodiment, when pressed, the cushion sheet acts to extrude bubbles and the like, and hence it is possible to effectively remove bubbles trapped between the print medium and the transfer sheet film, thereby ensuring reliable intimate contact between the two. It should be noted that the cushion sheet is preferably formed of a material such as silicone, urethane, vinyl chloride, or the like.
Preferably, the image-forming method further includes the step of forcibly cooling the print medium between the transferring step and the step of removing air.
According to this preferred embodiment, after the image transfer is completed, the print medium is rapidly cooled. This makes it possible to properly prevent warpage of the print medium which might be caused owing to heating, and at the same time, there occurs no problem in handling the print medium after the image transfer since the print medium can be cooled sufficiently.
Preferably, the image-forming method further includes the step of forcibly cooling the print medium between ending of the step of heating and ending of the step of pressing in the transferring step.
According to this preferred embodiment, it is possible to rapidly cool the heated print medium after the image transfer, thereby reliably preventing warpage of the print medium due to heating.
Preferably, the step of removing the at least one sheet of the transfer sheet film includes dissolving the transfer sheet film in water.
According to this preferred embodiment, since the transfer sheet film can be dissolved by immersion in water, it is possible to remove the transfer sheet film from the print medium very easily. Further, since the original image faintly left on the transfer sheet film can be caused to completely disappear, it is possible to prevent forgery of the print medium.
Preferably, the printing step includes printing the image by an ink jet printing method.
According to this preferred embodiment, it is possible to print a clear image. Particularly in color printing, the ink jet printing method is more advantageous than the thermal sublimation printing method using ink films of the three primary colors, in that it is possible to reduce ink usage and increase printing speed as well as to obtain an image with high resolution.
Preferably, the transfer sheet film is formed of a material which exhibits slight curability when heated.
According to this preferred embodiment, it is easy to remove the transfer sheet film after the heat treatment. Further, even when pressed and heated, the transfer sheet film do not adhere to the press means, and hence it is possible to prevent degradation of quality of the transfer image.
Preferably, the print medium is a card.
According to this preferred embodiment, it is possible to form a high-quality image on the card. For example, a photographic image for use on a license or certificate can also be formed without color irregularity or blur.
To attain the above object, according to a second aspect of the invention, there is provided a transfer sheet film for use in an image-forming method comprising the steps of:
printing an image on a printing surface of at least one sheet of the transfer sheet film prepared in a manner associated with at least one surface of a print medium, by using a sublimable dye ink, thereby causing the sublimable dye ink to be held in the at least one sheet of the transfer sheet film,
overlaying the at least one sheet of the transfer sheet film to the print medium such that the printing surface of the at least one sheet of the transfer sheet film faces the at least one surface of the print medium,
transferring the image by heating the at least one sheet of the transfer sheet film and the print medium overlaid to each other while applying pressure thereto, thereby causing diffusion of the sublimable dye ink held in the at least one sheet of the transfer sheet film into the at least one surface of the print medium for color development, and
removing the at least one sheet of the transfer sheet film from the print medium having the image formed thereon,
wherein the transfer sheet film is formed of a water-soluble and soft resin material, and the printing surface is formed to be a smooth surface.
According to the second aspect of the invention, temporary impregnation of the transfer sheet film with ink can be achieved reliably and stably. Further, it is possible to improve intimate contact between the transfer sheet film and the print medium, thereby forming a high-quality transfer image.
To attain the above object, according to a third aspect of the invention, there is provided an image-forming apparatus comprising:
printing means for printing an image on a smooth printing surface of a transfer sheet film formed of a water-soluble and soft resin material, by using a sublimable dye ink, thereby causing the sublimable dye ink to be held in the transfer sheet film;
overlay means for overlaying the transfer sheet film to a print medium such that the printing surface of the transfer sheet film faces a surface of the print medium; and
heating and pressing means for heating the transfer sheet film and the print medium overlaid to each other while applying pressure thereto, thereby causing diffusion of the sublimable dye ink held in the transfer sheet film into the surface of the print medium for color development, to cause transferring of the image,
wherein the heating and pressing means comprises a thermal press for sandwiching and heating the transfer sheet film and the print medium overlaid to each other.
According to this image-forming apparatus, since the transfer sheet film formed of a water-soluble resin material is employed as a transfer medium, it is possible to maintain excellent ink absorbency in a printing process, which allows the sublimable dye ink to be stably impregnated into the transfer sheet film and held in the same without being diffused. Further, since the printing surface of the transfer sheet film has smoothness, and the transfer sheet film is formed of a soft resin, uniform pressure and efficient heat treatment can be applied onto the whole surfaces of the transfer sheet film and the print medium which are in as intimate contact as possible by the thermal press method. This ensures reliable achievement of quick and faithful ink transfer in a state of diffusion of the ink toward the periphery of the transfer sheet film being prevented. It should be noted that the transfer sheet film is preferably formed of a material composed of a principal component of PVA (polyvinyl alcohol) and an additive which exhibits slight tackiness when pressed and heated.
Preferably, the image-forming apparatus includes control means for controlling pressing operation and heating operation of the thermal press separately, and the control means controls the heating and pressing operation of the thermal press such that a start of heating is delayed in timing with respect to a start of pressing.
According to this preferred embodiment, it is possible to remove a small amount of remaining air or microscopic bubbles from the interface between (or between contact surfaces of) the print medium and the transfer sheet film before ink transfer by heating actually starts. As a result, in heat and press treatments for heating and pressing the print medium and the transfer sheet film, the ink is transferred in a state of the print medium and the transfer sheet film being held in highly intimate contact with each other, which makes it possible to more reliably prevent microscopic asperities from being produced on the transferred image, thereby giving a gloss to the image. It should be noted that heating temperature is preferably adjusted such that it increases progressively.
More preferably, the image-forming apparatus further includes a cooling fan under control of the control means, for cooling the print medium after the heating and pressing operation of the thermal press, and the control means causes the cooling fan to start operation, after causing the thermal press in pressure contact with the print medium to stop heating.
According to this preferred embodiment, the print medium having the image transferred thereto is cooled by the cooling fan in a state held in the thermal press. Therefore, it is possible to minimize waste of time and cool the print medium sufficiently. In addition, warpage of the print medium due to heating can be properly prevented.
Preferably, a pair of heat-resistant plates each having a flat shape are interposed between the thermal press and the print medium, for sandwiching the print medium, and the pair of heat-resistant plates have soft cushion sheets laminated on respective surfaces thereof opposed to each other.
According to this preferred embodiment, treatments by the thermal press are performed via the pair of heat-resistant plates and the cushion sheet. As a result, the print medium can be held by the pair of heat-resistant plates in a sandwiched manner even when a presser of the thermal press has been lifted after the heat treatment, so that it is possible to prevent warpage of the print medium effectively. It should be noted that each heat-resistant plate is preferably formed of a material having high thermal conductivity and diffusivity.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.